The present invention relates to a method and apparatus for proportioning the contents in the manufacture of packing containers formed from tubular, flexible packing material. More specifically, the present invention relates to a method and apparatus for proportioning contents which are fed to a container which is then flattened, sealed and cut off below the surface of the contents.
Packing containers for e.g. milk or other, in particular liquid, foodstuffs are manufactured generally from laminated, flexible material which comprises layers of paper and thermoplastics. A known packing container is formed in that a laminate web, while being fed through the packing machine, is successively converted to tubular shape by joining together its two longitudinal edges and sealing them to one another in a liquid-tight manner. The tube so formed is moved substantially vertically downwards through the machine at the same time as contents are furnished via a fill pipe introduced into the upper, open end of the tube and extending downwards inside the tube. At the lower end of the tube the machine is provided with reciprocating processing jaws, co-operating with one another, which press together the passing material tube at regular intervals so that transverse flattened zones are produced wherein the walls of the material tube are sealed to one another in a liquid-tight manner. The transverse sealing of the material tube takes place below the level of the contents, and the tube is thus converted to coherent, substantially cushion-shaped packing containers which are completely filled with contents. After the cushion-shaped packing containers have been separated from one another through cuts in the transverse sealing zones, a final form-processing takes place so that the packing containers obtain the desired, e.g. parallelepipedic shape.
During the flattening of the packing material tube as well as the subsequent form-processing for converting the cushion-shaped packing containers to parallelepipedic shape, the contents are used as an internal "mandrel" or holder-up in the packing container. That is, the contents generate the internal back pressure which is necessary for making possible the forming of the packing container without undesirable deformation.
The principle of making use of the contents as a holder-up in the forming process has worked excellently up to now, since the packing containers have been manufactured so as to be completely filled with incompressible liquid contents, that is to say without air space. If packing containers with air space (so-called headspace) are to be manufactured, the contents do not produce the same well-defined and stable back pressure over the whole surface of the packing container and this increases the risk of creasing or other deformations. The technique of manufacture described above has proved less appropriate up to now, therefore, for the manufacture of packing containers of the partially filled type.
It is an object of the present invention to overcome the above-mentioned disadvantages and to provide a technique which makes it possible to manufacture and form partially filled packing containers with satisfactory results without having the packing containers being incompletely shaped or deformed.
It is a further object of the present invention to provide a method making possible an accurate proportioning of the quantity of contents in each packing container.
It is a further object of the present invention to provide a method which can be used in existing packing machines without appreciable complication.
These and other objects have been achieved in accordance with the invention in that a method for proportioning contents includes the mixing of the contents with gas prior to being fed into the packing material tube.
It is also an object of the present invention to provide an apparatus for proportioning contents which is simple and reliable in operation and capable of being combined with known types of packing machines.
These and other objects have been achieved in accordance with the invention in that an apparatus for proportioning contents includes a gas feed pipe which is joined to the fill pipe at some distance from the opening of the fill pipe.
The method and the apparatus in accordance with the invention provide a number of advantages in that they overcome the aforementioned disadvantages and make is possible to utilize known principles of package forming for the manufacture of packing containers which are only partially filled with contents. The volume of contents can be regulated in each individual packing container with great accuracy in a simple manner through variation of the quantity of gas fed. By choosing a suitable type of gas which is not harmful to the product, the method can be used with practically all types of contents.